(1) Field of the Invention
The invention, relates to the fabrication of integrated circuit devices, and more particularly, to a method of creating a fine pitch, high-density solder bump.
(2) Description of the Prior Art
With continuously decreasing semiconductor device dimensions and increasing device packaging densities, the packaging of semiconductor device continues to gain increased importance. Metal interconnects, thereby including points of metal contact such as solder bumps, which connect semiconductor devices to surrounding circuits, have therefore become of relative more importance.
The increasing need for creating device interconnect traces or networks has led to the application of low resistance metals, such as copper, for the interconnect traces while dielectrics having a low dielectric constant or other interfacing layers such as air gaps or cavities are increasingly used in between signal lines. Another approach to solve problems of I/O interconnect capability has been to design chips and chip packaging methods that offer dependable methods of increased interconnecting of chips at a reasonable manufacturing cost. This has led to the development of Flip Chip Packages.
Flip-chip technology uses bumps (typically comprising Pb/Sn solders) formed over aluminum contact pads on the semiconductor devices and interconnects the bumps directly to a packaging media, which are usually ceramic or plastic or organic material based. The flip-chip is bonded face down to the package medium through the shortest paths. These technologies can be applied not only to single-chip packaging, but also to higher levels of packaging, in which the packages are larger, and to more sophisticated substrates that have multiple layers of interconnect traces and that can accommodate several chips to form larger functional units.
The flip-chip technique, using an area I/O array, has the advantage of achieving a high density of interconnect to the device combined with a very low inductance interconnection to the package. The packaging substrate is generally used for Ball Grid Array (EGA) packages but can also be used for Land Grid Array (LGA) and Pin Grid Array (PGA) packages.
The mounting of a flip chip over the surface of a printed circuit board consists of attaching the flip chip to this board or to any other matching substrate. A flip chip is a semiconductor chip that has a pattern or array of terminals spaced around the active surface of the flip chip, the flip chip is mounted with the active surface of the flip chip facing the supporting substrate. Electrical connectors that are provided on the active surface of the flip chip can consist of Ball Grid Arrays (BGA) devices and Pin Grid Arrays (PGA) devices. With the BGA device, an array of minute solder balls is disposed over the active surface of the flip chip for attachment to the surface of a supporting substrate. For PGA devices, an array of small pins extends essentially perpendicularly from the active surface of the flip chip, such that the pins conform to a specific arrangement on a printed circuit board or other supporting substrate for attachment thereto. The flip chip is bonded to the printed circuit board by refluxing the solder balls or pins of the flip chip.
With the continuing decrease in the size of the contact pads that are used to connect pre-solder bumps thereto, the pitch of the solder bumps becomes increasingly more important. The invention addresses this issue and provides a method that significantly improves the pitch of the solder bumps that interface between a semiconductor device and the device supporting substrate over which the device is mounted.